Abstract: The Undiagnosed Disease Network (UDN) is motivated by the dual goals of providing a diagnosis to patients who have undergone a protracted unsuccessful diagnostic odyssey and by the opportunities for scientific discovery that these unique patients offer. The UDN's impact also extends to systematizing the approach to the undiagnosed patient. To date, the Pacific Northwest, 25% of the U.S. landmass and with significant expertise, has not had a clinical site in the UDN. We propose to fill this gap. Our PNW UDN team has deep and broad expertise across all the areas relevant for evaluating and diagnosing patients who have had a previously unproductive clinical diagnostic odyssey. Foremost, we have a diverse team of expert adult and pediatric clinicians, including more than 20 medical geneticists. We also have special expertise across broad areas of medicine including neurogenetics, dysmorphology, connective tissue disorders, and environmental health, as well as immunological, rheumatological, and dermatological conditions that will benefit the national UDN program. The proposed PNW UDN has internationally recognized expertise in novel pathogenic gene identification. Additionally, our expertise across a breadth of disciplines including pharmacogenetics, environmental genetics, translational bioinformatics, bioethics, healthcare outcomes, and policy will strengthen the UDN. The Specific Aims are: Aim 1: Provide broad expert diagnostic services, including deep phenotyping, to determine the cause of and treatment options for undiagnosed diseases in adults and children. Aim 2: Provide unique national expertise to enhance clinical and discovery capabilities within the UDN. Aim 3: Facilitate UDN disease discovery and knowledge dissemination outside of the UDN.